ARTIFACTS RELATED TO SAMPLE INTRODUCTION IN CAPILLARY GEL-ELECTROPHORESIS AFFECTING SEPARATION PERFORMANCE AND QUANTITATION

Two injection-related artifacts with capillary gel electrophoresis (CGE) are reported. The first occurs with consecutive injections from the same, low-volume (10-200 mu L), aqueous sample: progressively smaller peak heights are obtained with each injection. This phenomenon is explained in qualitative terms by examining the electrochemical processes occurring during the electrokinetic sample introduction. A simple solution to this problem is to perform an intermediate electrokinetic injection from a water vial prior to the sample injection. This two-step injection procedure results not only in dramatically increased precision (important for quantitative studies) but also in increased sample loading. The second artifact observed in CGE is related to the physical shape of the inlet of the gel-filled capillary: employing an oblique edge capillary results in poor performance, peak distortion, and loss in resolution.